The present invention relates to a magnetic bubble memory with a hybrid junction and more specifically deals with the junction enabling the propagation of a magnetic bubble from an area with non-implanted patterns to an area with deposited patterns. Throughout the remainder of the text such a junction will be designated IP or JIP junction for an implanted permalloy junction.
In a magnetic bubble memory, the magnetic bubbles are contained in a monocrystalline magnetic layer, such as a magnetic garnet film supported by an amagnetic monocrystalline garnet. These bubbles are in the form of generally cylindrical, isolated magnetic regions having a magnetization which is opposite to that of the remainder of the monocrystalline magnetic layer. These magnetic bubbles are stable through the application of a continuous or d.c. magnetic field H.sub.pol perpendicular to the plane of the magnetic layer. In practice, this magnetic field is produced by a permanent magnet, which consequently ensures the non-volatility of the informations contained in the bubble memory.
The bubbles are displaced by applying a rotary d.c. field H.sub.T in a direction parallel to the surface of the magnetic layer. The bubbles are displaced around the so-called propagation patterns.
These patterns are in the form of disks, lozenges triangles, T's, etc and can be produced from a material based on iron and nickel, deposited on an insulating layer covering the magnetic layer, or can be obtained by implanting ions in the upper part of the magnetic layer through a mask making it possible to define the shape of these patterns. In the latter case, in view of the fact that ion implantation is only carried out around these patterns, the latter are called non-implanted patterns.
The propagation patterns are generally contiguous and as a result of their shape, two adjacent patterns define two cavities or hollows between them.
The displacement of the bubbles along these patterns generally takes place for a time equal to one third of the rotation period of the planar magnetic field H.sub.T, the bubbles remaining stationary in the cavities defined between two adjacent patterns for the remainder of the cycle. These cavities constitute so-called stable positions. Thus, shift registers are produced in which the binary information 1 is represented by the presence of a bubble and the binary information 0 is defined by the absence of a bubble.
Apart from these propagation patterns, it is necessary to use electric conductors for producing within the bubble memory functions such as writing, information recording, non-destructive reading, transfer between registers and erasing.
FIG. 1 diagrammatically shows the known structure of a magnetic bubble memory. It comprises a group of so-called minor loops for storing informations parallel to one another and disposed along an easy magnetization axis 112 of the magnetic material. Each minor loop is connected by an exchange gate 4.sub.1 . . . 4.sub.n to a major writing loop 6 having at one end a magnetic bubble generator 8. The major writing loop 6 is aligned along an axis perpendicular to the axis of the minor loops. Each exchange gate makes it possible to write informations into a minor loop.
Each minor loop is also connected by a duplication gate 10.sub.1 . . . 10.sub.n to a major reading loop 12 parallel to the major writing loop 6. The major reading loop 12 is terminated by a detector 14 constituting a reading means.
A hybrid magnetic bubble memory has two regions 16, 18 with deposited patterns and a region 20 having non-implanted patterns. All the elements of the bubble memory are solely contained in regions 16, 18, with the exception of the minor loops, each of which extends over the three regions. Thus, each minor loop has four junctions JPI-E, JIP-E, JIP-D and JPI-D, which constitute the junctions between the propagation paths or tracks located in the different regions.
The invention relates to junctions enabling a magnetic bubble to pass from a propagation track defined by non-implanted patterns to a propagation track defined by deposited patterns, i.e. junctions JIP-E and JIP-D in FIG. 1.
Such junctions are more particularly described in patent application No. EP-A2-0 081 215, filed on Dec. 3, 1982 by HITACHI. FIGS. 2 and 3 respectively show junctions IP-E and IP-D according to the teaching of said specification.
In each drawing, a first propagation track is defined by a boundary 22 between an implanted area 24 and a non-implanted area 26 and a second propagation track is defined by a sequence of deposited patterns, such as deposited patterns 28, 30. The two propagation tracks have generally parallel directions and overlap at the first deposited pattern 28.
In European application No. 0 081 215 no information is given on the shape or size of the overlap zone, or on the orientation of the boundary between the implanted area and the non-implanted area level with said overlap zone.
However, embodiments of said junction have been described in several other documents.
In the article "Characteristics of junctions between ion-implanted and permalloy tracks in hybrid bubble devices" by N. KODAMA et al, published in IEEE Transactions on Magnetics, vol MAG20, No. 5 (part 1), September 1984, a junction IP-E is shown in FIG. 1. This junction is similar to that shown in FIG. 2, but the boundary between the implanted area and the non-implanted area has a step at overlap zone 32 and then the boundary continues as in FIG. 2.
The author states that this junction is not very reliable. Thus, it has been found that the field margin H.sub.pol was difficult to reproduce and that its value could vary between 4 and 10%, as a function of the memories. Moreover, the alignment between technological levels can lead to a deterioration of the margins.
The author proposes an improvement to the junction consisting of replacing the clearly defined boundary between implanted area 24 and non-implanted area 26, where the density of implanted ions passes suddenly from a non-zero value in the implanted area to a zero value in the non-implanted area, by a gentler boundary having a non-zero width where the density of the implanted ions decreases linearly from a non-zero value in the implanted area to a zero value in the non-implanted area.
An IP junction is also described in U.S. Pat. No. 4,546,452 granted on Oct. 8, 1985 to HITACHI. In this junction, the overlap between the two propagation tracks takes place over a length at least equal to 2.5.lambda., in which .lambda. is the spacing of the non-implanted patterns and said overlap zone is directed along an axis perpendicular to the general direction of the two propagation tracks.
The invention aims at obtaining a reliable IP junction, i.e. having a large, reproducible field margin H.sub.pol without having to use a gentle boundary.
In an IP junction, a magnetic bubble passes from a propagation track defined by non-implanted patterns to a propagation track defined by deposited patterns. In the overlap zone of the propagation tracks, it is consequently necessary to have a weak position in the implanted area and a stronger position on the deposited pattern, namely for the phase of the rotary field corresponding to the passage of the magnetic bubble from the first track to the second track.
According to the invention, to obtain a non-stable position in the implanted area at the time of the passage of the magnetic bubble, the boundary between the implanted area and the non-implanted area is oriented perpendicular to an easy magnetization axis of the magnetic material. Moreover, in order to be less sensitive to the alignment between the technological levels defining the two propagation tracks, the overlap zone between the implanted area and the deposited pattern has a surface substantially equal to that of the magnetic bubble.
With regard to the deposited pattern, it is known for the purpose of having a strong position on the pattern deposited level with the overlap zone, to use a pattern having the general shape of a chevron and whereof one leg has a particularly great length and width. According to the invention, it is proposed to increase the magnetic pole created level with the overlap zone by said reinforced arm by forming an implanted area beneath a significant part of said leg. This area has two functions, the first being to limit the width of the non-implanted area in the vicinity of the overlap zone, which reduces the stability of the magnetic bubble on the first propagation track level with said overlap zone, whilst the second function is to force the magnetic bubble towards the end of the other leg of the chevron, whilst in said implanted area the magnetic bubble tends, after extending between the overlap zone and the end of the other leg of the chevron, to return towards the overlap zone if certain technological parameters vary.